Download or read book Kinetic and Mechanistic Studies of the Hydroxyl Radical Initiated Photo oxidation of Saturated Hydrocarbons Under Simulated Atmospheric Conditions written by and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mechanistic Studies on the OH initiated Atmospheric Oxidation of Selected Aromatic Hydrocarbons written by Sascha Nehr and published by Forschungszentrum Jülich. This book was released on 2012 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A DOAS Study on the Oxidation Mechanism of Aromatic Hydrocarbons Under Simulated Atmospheric Conditions written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this work was to improve the understanding of the OH-radical initiated oxidation of aromatic hydrocarbons (benzene, toluene, p-xylene (BTX) and 1,3,5-trimethylbenzene (TMB)). These mechanisms are considered a major uncertainty in state-of-the-art photochemical models as they are used to predict photooxidant formation from urban air. Differential Optical Absorption Spectroscopy (DOAS) was employed in a systematic outdoor smog-chamber study at the European Photo Reactor (EUPHORE) located at the CEAM-Institute, Valencia/Spain. The available DOAS system was improved for this purpose. The yields of ring-retaining products (phenol from benzene, phenol-type and aldehyde-type compounds from p-xylene and TMB) and glyoxal (from BTX) were investigated. The phenol yield (Y(PHEN)= 53) was found more than two times higher than presently available literature values. Further, the bicycloalkyl-radical pathway was identified as a major pathway from BTX. It was demonstrated that the results of this study are representative for the atmosphere. Deviations from the the degradation pathways of BTX and TMB were further observed under conditions of high NOx (e.g. several ppm). The results of this work indicate that the representations of aromatics in photochemical models need to be updated. The results indicate that the contribution of aromatic hydrocarbons to the formation of photooxidants (i.e. ozone) is underestimated today.

Download or read book Mechanistic Studies of Atmospheric Chemical Reactions of Hydroxyl Radicals with Aromatic Hydrocarbons Including 2 ring Polycyclic Aromatic Hydrocarbons and Terminal Alkenes written by Noriko Nishino and published by . This book was released on 2009 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Kinetics and Mechanisms of the Hydroxyl Radical Initiated Oxidation of Oxygenated Volatile Organic Compounds Under Simulated Tropospheric Conditions written by Konrad Stemmler and published by . This book was released on 1998 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Hydroxyl Radical Initiated Oxidation of Unsaturated Hydrocarbons in the Troposphere written by Erin Elizabeth Tullos and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Isoprene is the dominant non-methane organic compound emitted by vegetation into the atmosphere, with a global emission rate of ~ 500 Tg yr-1. Its oxidation serves as a major source of ground level ozone in North America during the summer months. Despite the significant impact on tropospheric chemistry, questions remain concerning the detailed oxidation mechanism. The initial step in the mechanism is the addition of OH to form four distinct isomers. The relative branching between these isomers influences the distribution of the final products. I present a comprehensive investigation into the mechanistic details of early steps in the oxidation mechanism of unsaturated hydrocarbons in the troposphere and employ theoretical and experimental techniques. To understand the detailed kinetics of the initial OH addition to unsaturated hydrocarbons, I first present a model developed for the ethylene-OH system. I present the details of a robust two-transition state model. I extend the developed two-transition state model to the case of OH addition to isoprene. Excellent agreement with observed temperature and pressure dependent rate constants affords a high confidence level in understanding of the kinetics and in the calculated branching ratio of the initial OH addition step. I then focus attention on the subsequent reactivity of the OH-isoprene adducts. Until recently, all four of the OH-isoprene adducts were supposed to have reacted with O2 via addition to form alkylperoxy radicals. Previous computational results suggest that two of the OH-isoprene adducts undergo an intramolecular cyclic isomerization followed by hydrogen abstraction by O2 to form stable carbonyl compounds. I have synthesized photolytic precursors, presenting a novel approach to probe the subsequent reactivity of individual hydroxyalkyl radicals. Initial verification of the cyclic isomerization pathway involved synthesis of the photolytic precursor corresponding to the 1,3-butadiene-OH adduct. A culmination of theoretical and experimental techniques allowed verification of the cyclic isomerization pathway. I synthesized the photolytic precursor, which provided a single isoprene-OH adduct. Employing laser photolysis/laser induced fluorescence, time-dependent multiplexed mass spectrometry, velocity map ion imaging, and theoretical techniques, we present the full characterization of the reactivity of the single isoprene-OH adduct in the presence of O2.

Download or read book Experimental Studies of Hydroxyl Radical Initiated Tropospheric Oxidation of Unsaturated Hydrocarbons written by Buddhadeb Ghosh and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The tropospheric oxidation of unsaturated hydrocarbons is a central issue in atmospheric chemistry. These hydrocarbons are emitted into the atmosphere from both natural and anthropogenic sources, and their atmospheric oxidation leads to different atmospheric pollutants, including ground level ozone, photochemical smog and secondary organic aerosols. Isoprene and 1,3-butadiene represent a biogenic and an anthropogenic hydrocarbon, respectively, which primarily undergo electrophilic addition of OH radical, followed by chain propagating radical reactions. Their oxidation is the major source for ground level ozone formation in both rural and urban area and understanding their chemistry is essential for regional air quality modeling. Until recently, most of the studies of isoprene chemistry have been non-isomer specific, reflecting the reactivity of combined pathways and therefore were insensitive to specific details of the isomeric pathways. An isomeric selective approach to studying unsaturated hydrocarbon oxidation is described in this dissertation. A synthesized precursor, whose photolysis can provide a route to the formation of energy selected single isomer in the isoprene oxidation pathway, enables the study of important channels that are difficult to unravel in non isomer specific experiments. The major addition channel in OH isoprene oxidation has been studied following the isomeric selective approach and using Laser Photolysis-Laser Induced Fluorescence (LP-LIF) as the primary experimental technique. The study reveals important information about the oxidative chemistry of the [delta]-peroxy radicals, accounting for about 20% of missing carbon balance in isoprene oxidation, and isomeric specific rate constants. A similar approach was applied to study the oxidation of 1,3-butadiene, and the photolytic precursor for the dominant hydroxy alkyl isomer in the OH initiated oxidation of 1,3-butadiene was synthesized. The subsequent experiments and analysis revealed detailed information about the oxidative chemistry accounting for approximately 26% of the missing chemistry. Finally, non isomeric selective OH cycling experiments were carried out on the1,3-butadiene system. By analyzing the OH cycling data with the combined information obtained from the isomeric specific studies of the two isomeric channels of 1,3-butadiene oxidation, the relative branching between the two isomeric channels of OH-1,3-butadiene oxidation was determined.

Download or read book Research Publications Report written by and published by . This book was released on 1988 with total page 586 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mechanistic Studies of Atmospheric Photo oxidation Reactions written by K. C. Clemitshaw and published by . This book was released on 1986 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A DOAS Study on the Oxidation Mechanism of Aromatic Hydrocarbons Under Simulated Atmospheric Conditions written by Rainer Volkamer and published by . This book was released on 2001 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Kinetic and Product Studies of the Hydroxyl Radical Initiated Oxidation of Dimethyl Sulfide in the Temperature Range 250 300 K written by Mihaela Albu and published by . This book was released on 2008 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Study of the Hydroxyl Radical Initiated Photooxidation of Volatile Organic Compounds and the Application of These Reactions written by Clifford Koenig and published by . This book was released on 2002 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Kinetic and Mechanistic Studies of the Oxidation of Biogenic Oxygenated Organic Compounds in the Atmospheric Aqueous Phase written by Tobias Otto and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Role of Alkyl Peroxy Radicals in Hydrocarbon Oxidation Between 303 750K written by Terence John Mitchell and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Alkylperoxy radicals are important intermediates formed during the oxidation of organic compounds in combustion and atmospheric environments. Because of their ubiquity, accurate kinetic, mechanistic and spectroscopic information are necessary in order to model combustion and atmospheric processes. A Molecular Modulation Kinetic Spectrometer (MMKS) and gas chromatographic analysis were used to confirm and extend available peroxy radical data. Bromine initiated photo-oxidation of isobutane, at 303K, provided a source of t-butylperoxy radicals. Subsequent radical reactions were inferred from the observed product distribution. Evidence of the importance of the t-butylperoxy radical reaction with hydrogen bromide, and of a terminating channel for the radical's self-reaction, were obtained. Bromine initiated photo-oxidation of hydrocarbons may provide a useful source of peroxy radicals difficult to generate by alternative methods. Azoethane and azomethane photo-oxidation provided sources of ethylperoxy and methylperoxy radicals respectively. MMKS experiments enabled kinetic and spectroscopic parameters to be extracted for the former radical and its self-reaction between 303-457K, and for the latter at 303K. In the case of the ethylperoxy radical, complementary end-product studies enabled mechanistic information to be extracted. End-product studies provided evidence of two decomposition channels for a -alkylperoxyalkyl radical, generated in the hydrogen chloride catalysed decomposition of di-t-butyl peroxide at 393K. Thermochemically favourable O-heterocycle formation predominated over the alternative decomposition channel to olefin. A chemical kinetic model to describe the gas-phase oxidation of propane at 'intermediate' temperatures was developed. The latter was used to investigate the enhancement of commercially valuable products by additive gas 'addition'. Of the two additives tested, carbon monoxide and hydrogen peroxide, the former appeared more promising in modifying, favourably, the chemistry of the system.

Download or read book Kinetics and Mechanisms of the OH Radical Initiated Oxidation of Volatile Organic Compounds Under Simulated Tropospheric Conditions written by Jürg Ernst Eberhard and published by . This book was released on 1994 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Kinetic and Mechanistic Studies of the Reactions of Hydroxyl OH Radicals with Tetrachloroethylene and Trichloroethylene Over an Extended Temperature Range written by LeAnn Birklid Tichenor and published by . This book was released on 1999 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Unimolecular Reaction of Hydroxyperoxyl Radicals in the Troposphere written by Sui So and published by . This book was released on 2016 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt: [Beta]-Hydroxyperoxyl radicals are formed during atmospheric oxidation of unsaturated volatile organic compounds (VOCs) such as isoprene. They are also important intermediates in the combustion of alcohols. In these environments the unimolecular isomerisation and decomposition of [beta]-hydroxyperoxyl radicals may be of importance. Results of ion-trap mass spectrometry generating a prototypical distonic charge-tagged [beta]-hydroxyalkyl radical anion •CH2C(OH)(CH3)CH2C(O)O- have been obtained by a collaborating research group. The subsequent reaction of the radical anion with O2 in the gas phase has been investigated under conditions that are devoid of complicating radical-radical reactions. In this thesis, quantum chemical calculations and master equation/RRKM theory modelling are used to rationalise the results and discern a reaction mechanism. Reaction is found to proceed via initial hydrogen abstraction from the [gamma]-methylene group and [beta]-hydroxyl group, with both reaction channels eventually forming isobaric product ions due to loss of either •OH + HCHO or •OH + CO2. Isotope labelling studies confirm that a 1,5-hydrogen shift from the [beta]-hydroxyl functionality results in a hydroperoxyalkoxyl radical intermediate that can undergo further unimolecular dissociation. Furthermore, facile decomposition of [beta]-hydroxyperoxyl radicals has been confirmed to yield •OH in the gas phase. Moreover, the influence of an anionic charge on the reaction chemistry of [beta]-hydroxyperoxyl radicals has been investigated by examining the molecular orbitals of a distonic [beta]-hydroxyperoxyl radical anion analogue •OOCH2CH(OH)CH2C(O)O-. Instead of following the conventional Aufbau principle, the radical anion exhibits a peculiar electronic arrangement, where the singly occupied molecular orbital (SOMO) is no longer the frontier orbital and carries energy lower than other doubly occupied molecular orbitals (HOMOs). This phenomenon is manifested as SOMO-HOMO conversion and is caused by the through space stabilisation between the interaction of the anion and radical site. Further investigation of the other C4H6O5•- isomers involved in the unimolecular reaction mechanisms of the hydroxyperoxyl radical anion •OOCH2CH(OH)CH2C(O)O- revealed that these radical anion isomers exhibit different extent of orbital conversion. As a result, the reaction chemistry of this radical anion is influenced by various additional stabilities associated with the unconventional electron arrangement, switching the dominant reaction pathway from [beta]-OH abstraction in the relevant neutral radical to C-H abstraction at the [beta]-carbon in the radical anion analogue. Despite the change in product distribution, all reaction pathways remain the same in both the neutral radical and radical anion analogues. Enols are emerging as trace atmospheric components that may play a significant role in the formation of organic acids in the atmosphere. They are unsaturated VOCs and their oxidation involves hydroxyperoxyl radicals as key intermediates. It has recently been discovered that acetaldehyde can undergo UV-induced isomerisation to vinyl alcohol (the enol counterparts) under atmospheric conditions. The •OH-initiated oxidation chemistry of vinyl alcohol has been investigated in this thesis, using quantum chemical calculations and energy-grained master equation simulations. The reaction proceeds by •OH addition at both the [alpha]-carbon (66%) and [beta]-carbon (33%) of the [pi] system, yielding the C-centred radicals •CH2CH(OH)2 and HOCH2C•HOH respectively. Subsequent trapping by O2 leads to the respective peroxyl radicals. About 90% of the chemically activated population of the major peroxyl radical adduct •O2CH2CH(OH)2 is predicted to undergo fragmentation to produce formic acid and formaldehyde, with regeneration of •OH. The minor peroxyl radical CH2(OH)CH(OH)O2• is even less stable and almost exclusively undergoes HO2• elimination to form glycolaldehyde. The •OH-initiated oxidation of vinyl alcohol ultimately leads to three main product channels, being (i) •O2CH2CH(OH)2 (8%), (ii) HC(O)OH + HCHO + •OH (56%) and (iii) HOCH2CHO + HO2• (37%). This study supports previous findings that vinyl alcohol should be rapidly removed from the atmosphere by reaction with •OH and O2, with glycolaldehyde being identified as a previously unconsidered product. Moreover, it is also shown that direct chemically activated reactions can lead to •OH and HO2• (HOx) recycling. Following the study on the acetaldehyde-vinyl alcohol pair, the photo-isomerisation of glycolaldehyde to 1,2-ethenediol has been studied. The keto-enol isomerisation is associated with a barrier of 66 kcal mol-1 and involves a double hydrogen shift mechanism to give the lower energy Z isomer. This barrier lies below the energy of the UV/Vis absorption band of glycolaldehyde and is also considerably below the energy of the products resulting from photolytic decomposition. The atmospheric oxidation of 1,2-ethenediol by •OH is initiated by radical addition to the [pi] system to give the •CH(OH)CH(OH)2 radical, which is subsequently trapped by O2 to form the peroxyl radical •O2CH(OH)CH(OH)2. According to kinetic simulations, collisional deactivation of the latter is negligible and cannot compete with rapid fragmentation reactions, which lead to (i) formation of glyoxal hydrate and HO2• through an [alpha]-hydroxyl mechanism (96%) and (ii) two molecules of formic acid with release of •OH through a [beta]-hydroxyl pathway (4%). The lifetime of the two enols in the presence of tropospheric levels of •OH is determined to be around 4 hours and 68 hours respectively. Phenomenological rate coefficients for these two oxidation reactions are obtained for use in atmospheric chemical modelling. Finally, photo-induced dissociation and isomerisation of other common tropospheric carbonyl compounds, namely methyl vinyl ketone (MVK) and methacrolein (MACR), has been reinvestigated. The reaction of both molecules proceeds through dissociation, cyclisation and hydrogen shift (including keto-enol isomerisation) pathways. From the simulation of reaction dynamics, MACR photolysis is significantly less efficient than MVK photolysis, which is consistent with the experimental data in the literature. Isomerisation dominates dissociation in the actinic spectrum at longer wavelengths for both MVK and MACR photolysis. The total photolysis rate of MVK and MACR is calculated to be 3.8 x 10-5 s-1 and 8.6 x 10-7 s-1 respectively. The study reveals that MVK and MACR photolysis may lead to formation of new atmospheric VOCs such as hydroxylbutadiene from MVK and dimethylketene from MACR.